1. Field of the Invention
The present invention relates to a process for producing a window glass with a thin film thereon.
2. Description of the Prior Art
Conventional methods for forming a thin film on a substrate include a spraying method on a substrate at a high temperature, and dip-coating, spin-coating and roll-coating methods on a substrate at room temperature, and the like. However, any of these conventional methods required to use a large amount of coating solution, which resulted in a high cost. Other methods such as vacuum vapor deposition and sputtering methods required a high apparatus cost and were poor in productivity.
Also, in the case of forming a thin film on only a part of a glass substrate, physical vapor deposition methods such as a vacuum deposition method and a sputtering method required masking on the substrate, which resulted in a high manufacturing cost and a poor productivity.
On the other hand, as a method without using a mask, a screen-printing method is enumerated. However, when a relatively large area of a glass substrate is printed, the screen-printing method is not preferable in the following respects.
That is, as shown in FIG. 16(a), in the case of the normal state of the screen-printing, a glass substrate 1 on a table 23 and a screen 20 supported by a screen frame 21 come in contact with each other under the force of a squeezer 22 in a straight line where an ink 24 oozes though the screen 20 and is printed on the glass substrate 1. However, in the case of printing a film of a large area, as shown in FIG. 16(b), the screen 20 is not clearly separated from the glass substrate 1 on the printing part even after the squeezer 22 passes, and when the the screen 20 is abruptly separated from the glass substrate 1 after printing, the printed pattern thus obtained becomes deformed and uneven. The printed pattern thus obtained forms an uneven film when the ink is dried or baked. When printing a ceramic color ink on the periphery of a glass substrate or when printing a paste for fine electroconductive print, the above mentioned troubles do not arise, but when printing a large area, the trouble as shown in FIG. 16(b) is caused. Also, in the screen-printing, the viscosity of an ink must be increased so as not to flow downwards. In order to increase the viscosity of the ink, the content of an organic material having a large molecular weight must be increased. Such a screen-printed layer containing the above mentioned organic material does not form a satisfactory film because gasses such as carbonic acid gas, water or N.sub.2 are evolved during baking. In other words, the thin film thus obtained becomes porous and therefore poor in wear resistance and chemical resistance, and is consequently unusable.